This invention relates to a method for continuously producing methyl tert-butyl ether in high yield by allowing an isobutylene-containing hydrocarbon mixture and methyl alcohol to react with each other in the presence of a catalyst. This invention further relates to the preparation of a fuel composition which is made by mixing the thus obtained methyl tert-butyl ether into an internal combustion fuel.
In recent years, there has arisen a social problem of environmental pollution with lead which is caused by the exhaust gases of internal combustion engines. As a result, regular gasoline has already been made lead-free completely and premium gasoline will also be made lead-free in due course. Hence, in order to produce unleaded gasoline while maintaining octane value as in the past and without varying the compounding ratio of basic gasoline, an octane value improving agent must be added to gasoline.
There are known many kinds of compounds as the octane value improving agents. Particularly, ethers having branched alkyl groups are well known as they have been disclosed in the Third World Petroleum Congress, Sec. VI, 397 (1951). For example, it is well known that the octane values of methyl tert-butyl ether (hereinafter referred to as "MTBE"), ethyl tert-butyl ether and isopropyl tert-butyl ether are very high.
With regard to the method for producing MTBE, it is known that MTBE is prepared by the reaction between methyl alcohol and isobutylene in the presence of a catalyst. Especially, proposed in some methods is the use of strongly acidic cation-exchange resin as a catalyst (cf. Japanese Patent Publication No. 34803 of 1973, Japanese Patent Laid-open Publication No. 61109 of 1974, Japanese Patent Laid-open Publication No. 58006 of 1975, and U.S. Pat. No. 2,480,940). In these conventional methods, however, an acid substance is extruded from the strongly acidic cation-exchange resin during the reaction so that the reaction mixture is accompanied by the acid substance. In addition, since the succeeding separation step of distillation is done with heating, the reverse reaction from MTBE to methyl alcohol and isobutylene is caused to occur as the MTBE has tertiary carbon atoms. Accordingly, the yield of MTBE is disadvantageously reduced. Further, the reaction product containing such acid substance cannot be mixed into fuel oil as it stands.